Digestive System #2

2 17.9: Small Intestine The small intestine is a tubular organ that extends from the pyloric sphincter to the beginning of the large intestine It completes digestion of the nutrients in chyme, absorbs products of digestion, and transports the remaining residue to the large intestine It consists of three parts that include: Duodenum Jejunum Ileum

3 Parts of the Small Intestine Stomach Jejunum Duodenum Ascending colon Mesentery Appendix Cecum Ileum Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

4 Stomach Small intestine © Armed Forces Institute of Pathology

5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Liver Stomach Gallbladder Transverse colon underneath Greater omentum

6 Structure of the Small Intestinal Wall Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lacteal Blood capillary network Intestinal gland Goblet cells Simple columnar epithelium Venule Arteriole Lymph vessel Villus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lumen Intestinal gland Villus © The McGraw-Hill Companies, Inc./Al Telser, photographer

7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Microvilli Cell membrane Mitochondrion Golgi apparatus Nucleolus Nucleus (a) LumenMicrovilli (b) Rough endoplasmic reticulum Cytoplasm of epithelial cell b: © The McGraw-Hill Companies, Inc./Al Telser, photographer

8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Submucosa Circular muscle Longitudinal muscle Serosa (a) (b) Plicae circulares Muscular layer Villi

9 Secretions of the Small Intestine In addition to mucous-secreting goblet cells, there are many specialized mucous-secreting glands (Brunner’s glands) that secrete a thick, alkaline mucus in response to certain stimuli Enzymes in the membranes of the microvilli include: Peptidase – breaks down peptides into amino acids Sucrase, maltase, lactase – break down disaccharides into monosaccharides Lipase – breaks down fats into fatty acids and glycerol Enterokinase – converts trypsinogen to trypsin Somatostatin – hormone that inhibits acid secretion by stomach Cholecystokinin – hormone that inhibits gastric glands, stimulates pancreas to release enzymes in pancreatic juice, and stimulates the gallbladder to release bile Secretin – stimulates the pancreas to release bicarbonate ions in pancreatic juice

10 Regulation of Small Intestinal Secretions Regulation of small intestine secretion occurs by: Mucus secretion is stimulated by the presence of chyme in the small intestine Distension of the intestinal wall activates nerve plexuses in the wall of the small intestine Parasympathetic reflexes triggering the release of intestinal enzymes

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12 Absorption of the Small Intestine Villi increase the surface area for absorption Small intestine absorption is so effective that very little reaches the organ’s distal end, noting that: Monosaccharides and amino acids absorb: Through facilitated diffusion and active transport Absorbed into blood Large proteins are broken down and absorbed into villi Fatty acids and glycerol absorb by: Several steps involved as noted Absorbed into lymph and blood Electrolytes and water absorb: Through diffusion, osmosis, and active transport Absorbed into blood

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14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MaltoseGlucose MonosaccharidesDisaccharide Glucose  HH O Maltase  HO H O OH H O H H HO H O OHHO H O H2OH2O Water HNC H H Amino acid Dipeptidase   R C H N O C R H HNC H H R COH O H N C H H R C O C O Dipeptidase H2OH2O Dipeptide (from protein digestion) Water Lipase H CHO H CH H CH C C 17 H 35 COO H H CH 3H 2 O Lipase ++ Fatty acidsGlycerolFat C H C H O C O C O C 17 H 35 COO Water C 17 H 35 C OH

15 Movements of the Small Intestine The small intestine carries on mixing movements that include: Peristalsis – pushing movements that propel chyme Segmentation – ring-like contractions that can move chyme back and forth

: Large Intestine The large intestine is named because of its diameter It has five parts that include: Cecum Colon Ascending, transverse, descending and sigmoid Rectum Anus

17 Parts of the Large Intestine Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anal canal Sigmoid colon Haustra Descending colon Rectum Appendix Cecum Orifice of appendix Ileocecal sphincter Ascending colon Serous layer Mucous membrane Transverse colon Muscular layer Ileum Hepatic flexure Tenia coli Splenic flexure Epiploic appendage

18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Jim Wehtje/Getty Images

19 Structure of the Large Intestinal Wall © Ed Reschke/Peter Arnold Lumen Submucosa Muscular layer Serosa Mucosa Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

20 Functions of the Large Intestine The large intestine: Has little or no digestive function Absorbs water and electrolytes Secretes mucus Houses intestinal flora Forms feces Carries out defecation Lumen of large intestine Goblet cells © Ed Reschke Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

21 Movements of the Large Intestine Movements of the large intestine are similar to those of the small intestine It is slower and less frequent than that of the small intestine Movements include: Mixing movements Peristalsis Mass movements usually follow meals The defecation reflex relaxes the internal anal sphincter and then the external anal sphincter

22 Feces Feces is composed of materials not digested or absorbed, and include: Water Electrolytes Mucus Bacteria Bile pigments altered by bacteria provide the color The pungent odor is produced by bacterial compounds including: Phenol Hydrogen sulfide Indole Skatole Ammonia

: Lifespan Changes Changes to the digestive system are slow and slight, and eventually include: Teeth may become sensitive Gums may recede Teeth may loosen, break or fall out Heartburn may become more frequent Constipation may become more frequent Nutrient absorption decreases Accessory organs age but typically not necessarily in ways that effect health